Known online systems for nitrate measurement or for measuring the content of organic substances are also available from Endress+Hauser under the mark STAMOSENS.
DE 199 02 396 C2 discloses an arrangement for measuring the nitrate content of liquids. In the case of this known arrangement, the radiation from a UV light source is split via two crossed, deflecting mirrors into parts traveling on two measurement branches in a measuring cuvette. One branch is for UV radiation reception and the other branch is for IR radiation reception. By measuring the nitrate concentration in the maximum (preferably at 214 nm) and in the minimum (preferably at 830 nm) of the nitrate absorption curve, a high measuring accuracy is achieved, since the arrangement of the two measuring branches with different wave lengths (two channel system) makes possible, in simple manner, the mathematical compensation of disturbing influences, such as clouding substances, aging effects of the light source and foulings of the cuvette.
In the case of known photometric measuring equipment, depending on the substance to be measured, either a wavelength-specific LED or a broadband light source is used. In the case of the broadband light source, the selection of the required wavelength is accomplished by an interference filter, which is arranged either after the light source or in front of the detector unit. The detector unit can be at least one photodiode, phototransistor or similar photoelectric component.